Several parallel eccentric gear trains for rotary actuators are known to the art. For example, U.S. Pat. No. 8,403,789 (Janek), assigned to Spinea S.R.O., discloses a gear train for a parallel eccentric rotary actuator which is reproduced in FIG. 20. The gear train disclosed therein includes a central ring gear 40, left and right end plates 50, a bearing ring 46, a seal 93, left and right cross links 80 equipped with spline grooves (not shown), a crankshaft bearing 10, radial axle bearings 43a, 43b, 43c, a cycloidal curve 30, needles 41b, and through bolts 95. Other gear trains by Spinea of this general type are described, for example, in 2013/0023373 (Janek) and U.S. Pat. No. 5,908,372 (Janek).
U.S. Pat. No. 7,604,559 (Fujimoto et al.), assigned to Nabtesco Corporation, discloses an eccentrically oscillating gear device. This device, which is depicted in FIGS. 21-23, is equipped with an internal gear 15 having internal gear pins 15a, a carrier 11 rotating relative to the internal gear, a pair of bearings 19, 20 that have rolling elements and a ring body for supporting the rolling element, a crank shaft supported by the carrier so as to be freely rotatable and external gears 13, 14 that are equipped with external teeth having a trochoid tooth profile whose tooth top portions are cut out, and disposed between the pair of bearings. The outer peripheries of the external gears are engaged with the internal gear pins and fitted to the crank portion of the crank shaft. The eccentrically oscillating gear device is designed so that the external gear makes an eccentrically oscillating motion by rotation of the crank shaft and the rotational output is taken out from the internal gear or the carrier.